Polymerization catalyst systems offer opportunities for providing new processes and products to various markets including those which utilize olefin polymerization materials. Accordingly, supported olefin polymerization catalyst systems are of interest in making new olefin polymerization materials and products available.
Supported catalyst systems useful for olefin polymerization which may be interest include those comprising a metallocene, which are referred to herein as metallocene catalysts and metallocene catalyst systems. As used herein, metallocene catalyst systems may include the combination of a metallocene catalyst precursor and an activator, and may also include a support. Supports useful with metallocene catalyst systems preferably comprise porous materials, and may include both organic and inorganic components.
Inorganic components that may be useful within or as a catalyst support, such as silica and/or alumina, may comprise reactive functionalities. These reactive functionalities, for example hydroxyl groups (i.e., —OH) may also prove beneficial within the catalyst system. For example, a concentration of active —OH groups can provide for association of one or more catalyst system components with the support. However, excess hydroxyl groups present within or on the support (i.e., hydroxyl groups not involved in providing for association of a catalyst system component) may deactivate the catalyst system. As a result, excess hydroxyl groups of a support may reduce the overall activity of a supported catalyst system. Accordingly, it is desirable for a support to comprise a number of hydroxyl groups which allows for association of one or more catalyst system components, and in addition, to remove, reduce or render inactive a sufficient number of the hydroxyl groups on a catalyst support to provide for an improved catalyst system activity.
The deactivation of a catalyst system which may result from free hydroxyl groups on a support can be overcome in a number of ways. For example, the deactivation of a catalyst system may be overcome through the addition of more catalyst, by increasing the catalyst concentration in the catalyst system, and the like. These approaches, however may be undesirable due to a substantial increase in the cost of olefin polymerization.
Other methods to overcome the deactivation of a catalyst system that result from free hydroxyl groups and other reactive functionalities present on a support, can include at least partially deactivating the support by removing and/or reducing the number of free hydroxyl groups present on the support. Such methods may include using thermal and/or chemical treatments directed towards removing and/or chemically binding with hydroxyl groups to thereby render free hydroxyl groups inactive.
Examples of thermal and/or chemical treatments directed towards deactivating, and/or reducing the activity of a catalyst supports (i.e., reducing the SiOH concentration on the support) include U.S. Pat. Nos. 6,525,988 and 6,368,999 to Speca, which are directed to deactivation of a silica catalyst support by calcining the silica in the presence of a fluorine source. The fluorided silica of Speca is reported to improve the support over silica supports that had been calcined without the fluoride source. It is also reported that the fluorided silica of Speca was an improvement over a support that had been calcined without fluoride, and had been subjected to chemical dehydration with hexamethyldisilazane. Other examples include WO2002/16455 and WO2002/216681, which are directed to isotactic polypropylene made using a metallocene catalyst system supported with fluorided silica. U.S. Pat. Nos. 6,355,594, 6,388,017, and 6,395,666 are directed to metallocene catalyst supported on fluorided silica, silica-alumina, and silica-titania, while WO2001/41920, WO2001/44308, WO2001/44309 and WO2001/58587 are directed to using fluorided silica-zirconia as a metallocene catalyst support.
Methods of deactivating a catalyst support using chemical means include U.S. Pat. No. 6,329,313 to Fritze et al., in which a silica catalyst support is deactivated by “chemical inertization” using alkylaluminum, -magnesium, -boron, or -lithium compounds such as a silyl chloride to render free hydroxyl groups inert. In one example, the support was dried at 200° C., and then treated with vinyltriethoxysilane prior to being contacted with an activator.
Other examples of chemical deactivation of supports include U.S. Pat. No. 5,324,698 to Ala-Huikku et al., which is directed chemically deactivating a silica support using triethylaluminum; WO2000/40623, directed to a metallocene catalyst on a support that has been passivated (i.e., deactivated) using Lewis acid alkylating agents such as trihydrocarbyl aluminum compounds, trihydrocarbylchlorosilane compounds, and trihydrocarbylalkoxysilane compounds; and U.S. Pat. Nos. 5,643,847, 5,972,823, 6,262,202, and 6,426,313 all of which include deactivation of silica by addition of the Lewis Acid (LA) activator in an amount in excess of the stoichiometric amount required to attach the catalyst to the support.
However, both chemical and thermal deactivation of a support material may fail to achieve a sufficient level of deactivation. Thus, there remains a need for a method to deactivate supports such that the support comprises hydroxyls at a concentration sufficient to associate components of a catalyst system (e.g., a number of hydroxyl groups sufficient to react with an activator), but which also have a concentration of free hydroxyl groups, if any, which do not detrimentally effect the overall catalyst system activity. Particularly, there remains a need for improved deactivation of silica based catalyst supports for use in metallocene catalyst systems, wherein the concentration of reactive functionalities present in or on the support are sufficiently reduced and/or deactivated thus providing for a supported metallocene catalyst system having an improved activity over that known in the art.
Other references of interest include:    1. U.S. Pat. No. 5,496,960 to Piers et al.    2. U.S. Pat. No. 6,265,505 to McConville et al.    3. U.S. Pat. No. 6,555,495 to Peterson et al.    4. U.S. Pat. No. 6,403,732 to Marks et al.    5. U.S. Pat. No. 4,808,561 to Welborn et al.    6. U.S. Pat. No. 6,552,137 to Kao et al.    7. U.S. Patent Application No. 20030008980 to Mawson et al.    8. U.S. Patent Application No. 20020082367 to McConville et al.    9. U.S. Patent Application No. 20010031695 to Loveday et al.    10. U.S. Patent Application No. 20010041778 to McConville et al.    11. PCT Patent Publication WO 00/13792 to Clark.